NGC 7009

THE SATURN NEBULA

In Aquarius

From Jim Kaler's STARS; Return to Planetary Nebulae

NGC 7009 NGC 7009
"Of wonderfully intricate structure" (Curtis), the planetary nebula NGC 7009, the "first planetary," displays a pair of jug-handle-like "ansae" that give it the name "The Saturn Nebula." On the left is a drawing made from a series of photographs, the gaseous nebula perhaps appearing as its discoverer William Herschel may have seen it.

In Herschel's words about his discovery object (from an article in the Philosophical Transactions of the Royal Society in 1785): "I shall conclude this paper with an account of a few heavenly bodies, that from their singular appearance leave me almost in doubt of where to class them. The first precedes Nu Aquarii 5'.4 minutes in time [5.4 minutes, 1.25 degrees], and is I' (minute of arc) more north ... The planetary appearance of the first two is so remarkable, that we can hardly suppose them to be nebulae; their light is so uniform, as well as vivid, the diameters so small and well defined, as to make it almost improbable that they should belong to that species of bodies." Thus was born the oft-confusing term, by which Herschel merely meant "disk-like." After all, who had a better right than the discoverer of the first planet since ancient times? (While Lyra's Ring Nebula was already known, it was not placed into the category of planetary nebulae until later.) Herschel then went on to discover (in NGC 6543) that planetary nebulae have central stars

On the right is a Hubble Space Telescope image made nearly a century later, showing the vast improvement in astronomical imagery as well as the immense complexity of the nebula. The hot (90,000 Kelvin), blue, 13th magnitude star at the center is the old nuclear-burning core of what was once an extended giant star, while the surrounding nebula is the inner part of the star's lost envelope that has been structured by the remaining star's hot wind. The distance is not well known. If at 2000 light years, the nebula is 3/4 of a light year long. The central star seems faint to us only because of its distance and because the vast majority of its radiation comes out as energetic ultraviolet light. In reality, the star thousands of times more luminous than the Sun. Still heating at constant luminosity, the star will eventually cool and dim to become one of the many white dwarfs that dot the cosmos.

The ansae, called "FLIERS," are high-speed jets shot out of the central star, probably along the star's rotation axis. While NGC 7009's are the most prominent, they are seen in a number of nebulae, notably NGC 3242, NGC 6543, and NGC 2371- 2. Their origins and significance are not understood.

Left: Image and quote by H. D. Curtis from Publications of the Lick Observatory, Volume 13, Part III, 1918. Right: B. Balick, J. Alexander (U. Wash.), A. Hajian (USNO), Y. Terzian (Cornell U.), M. Perinotto (U. Florence), P. Patriarchy (Arcetry Obs.), and NASA.